The present invention relates to a constant voltage circuit for use in an RFID tag chip or the like and, more particularly, to a process of starting power at the time of start-up.
In recent years, the number of chips operating on power received from electric waves is increasing. One of such chips is an RFID tag chip (hereinbelow, called RFID tag chip). One of uses of the RFID tag chip is to identify a person or object by radio.
Basically, unique numbers are assigned to all of RFID tag chips. A reader/writer can read a unique number by radio communication. Since the operation of associating numbers and chips is performed on the reader/writer side, an RFID tag chip itself does not have a complicated function. According to a demand, an RFID tag chip has only the function of outputting a number assigned to the chip. Some products have the function of storing information and the security function.
The functions of an RFID tag chip are relatively simple. However, when it is assumed that the RFID tag chip is used in place of a bar code, the RFID tag chip is demanded to be producible at very low lost. In 2008, the immediate goal of the manufacturing cost of the RFID tag chip is about 5 yen per unit.
Since the RFID tag chips operate on electromotive force of electric waves, many of the RFID tag chips have to operate at very low power consumption.
Many RFIDs use electric waves in the bands of 13.56 MHz, 900 MHz, and 2.4 GHz. A main target of the present invention is a standard called EPC Global Class 1 Generation 2 (C1G2 or EPC Gen2) used mainly in the 900 MHz band. Introduction of the standard started in major retailers in all over the U.S.A. and major electronics retail stores in Japan and is already a de facto standard. At present, the standard is mainly applied in distribution. The market scale when an RFID tag is attached to each commodity in future is large.
An RFID tag conformed with the EPC Gen2 can make communication with a distance of 3 m or longer using electric waves of 900 MHz. Based on this point, there are some technical characteristics. First, considering the communication distance of 3 m, the RFID tag has to operate on very low current. The entire chip has to operate on a current of about 10 μA.
Considering mechanical strength when a tag chip is used as an inlet, desirably, the tag chip has a size of a certain degree of area.
Due to the above, as reference power circuits employed for a general RFID tag chip, a BGR (Band Gap Reference) circuit and a threshold-difference-using-type reference voltage generating circuit (Vth difference reference circuit) exist. The circuits are used since they are relatively cheap and their mount areas are small.